River regulation and recruitment in a protracted‐spawning riverine fish

Abstract

We present and test an extension of the "match/mismatch" hypothesis that attempts to explain the persistence, under conditions of flow alteration, of small, short-lived, native, riverine, fish species. The premise is that flow alteration typically changes environmental conditions, such as temperature and prey abundance, which may affect survival during the larval period of fishes. This "window-of-opportunity hypothesis" states that, if optimal conditions for recruitment vary temporally within a year, the probability that a proportion of the larvae of protracted-spawning species will encounter a period of optimal conditions is greater than for larvae with only a brief spawning period, and so the former will have a recruitment advantage. We determined whether all hatching events contributed equally to juvenile recruitment of the protracted-spawning Australian smelt (Retropinna semoni) during one breeding season in three pairs of heavily regulated and largely free-flowing unregulated rivers in the Murray-Darling Basin, Australia, and related patterns in the hatch dates of recruits to temperature or prey biomass for one pair. For all rivers, heavily regulated or not, recruits present at the end of the breeding season most commonly hatched in the latter part of the breeding season. Mortality of those fish hatched in the first part of the season likely explains this trend. Furthermore, while hatching times were similar for all rivers, each river showed a distinct pattern of hatching and recruitment, which may relate to the temperature range within which epigenetic processes are aligned. Patterns of zooplankton biomass differed between the largely free-flowing ovens and regulated Goulburn rivers and likely had different sources: within the channel and within the storage lake, respectively. For the Ovens River, recruits hatched subsequent to the period when the first significant increase in zooplankton biomass occurred. We hypothesize that temperature may largely influence the "window" during which recruitment can take place but that prey density, responding to river-specific interactions between temperature and discharge, plays a role in the timing and magnitude of recruitment of Australian smelt. We conclude that the match/mismatch hypothesis may be applicable to rivers, that the window-of-opportunity hypothesis has some currency and deserves further investigation, and that river regulation may have significant impacts on fish recruitment.

Patterns and processes in the drift of early developmental stages of fish in rivers: a review

“…reproductive effects; Zitek et al 2004a) or because larvae do not survive (i.e. recruitment effects; Schiemer et al 2001;Humphries et al 2013), temperature and discharge not only govern the timing, but also the spawning success and hence the subsequent intensity of larval drift (Reichard et al 2002b;Durham and Wilde 2008;Ellsworth et al 2010b). Intra-and inter-annual variation in drift densities, for instance, may be attributed to fluctuations in water temperature and the related variability in egg mortality during incubation (Busch et al 1975;Sonny et al 2006).…”

Exploitation by Common Carp (Cyprinus Carpio) of A Floodplain Wetland of The Lower River Murray Under Drought and Flooding Conditions

“…as a result of this extended 'window of opportunity' (sensu Humphries et al 2013), it has been hypothesised that carp may spawn twice annually, that is once at the onset of the breeding season and again after re-maturation of the gonads three to four months later (i.e. January/February) (Smith & Walker 2004b;Smith 2005 YoY, which eventually leave these areas to enter the main channel and disperse after reaching a size of 50-100 mm tL ( this finding is in agreement with the reported lower asymptotic sizes but faster growth rates for carp in australia compared to other parts of the world (Weber & Brown 2009)-even though individuals falling in the two upper size categories (i.e.…”

Movement patterns and rheoreaction of larvae of a fluvial specialist (nase, Chondrostoma nasus): the role of active versus passive components of behaviour in dispersal

“…The reduction of characteristic and native riverine fish fauna mainly due to pervasive habitat alteration is a worldwide phenomenon that has been acknowledged for decades (Schiemer and Spindler 1989), but is still ongoing (Moyle and Mount 2007). A greater understanding of dispersal processes will contribute to our understanding of recruitment and will certainly aid future conservation measures targeting the growing number of endangered riverine fish populations (Cooke et al 2012;Humphries et al 2013;Lechner et al 2016). Wellperforming models of the migration of fish larvae from spawning to nursery areas could present an invaluable tool in designing effective river restoration measures in the 21st century.…”